This project is designed to investigate the mechanisms involved in the induction and maintenance of nonresponsiveness, or tolerance, in helper-type T cells. Deletion of T cell reactivity to self antigens is not well understood, and impairment of self-tolerance can result in autoimmune diseases such as systemic lupus erythematosus and arthritis. An efficient in vitro method for the induction of tolerance in cloned, murine helper T cells has been developed, allowing analysis of T cell responses to tolerogens in the absence of contaminating cells. Culture of T cell clones with specific antigen and the appropriate la molecule purified from la- bearing cells results in the long-lived inability of T cells to produce lL-2 or to proliferate to subsequent antigen-specific stimulation. However, tolerant T cells retain antigen-receptor expression and can produce lL 3 after activation. This in vitro method of tolerance induction will be applied to normal, uncloned, resting T cells to determine whether direct inactivation for proliferation is also a mechanism for nonresponsiveness in normal cells. Antibodies reactive with the T cell antigen-receptor or with CD3 proteins, that are thought to form the signal-transducing complex for specific T cell activation, will also be tested as tolerogens. The functional properties of tolerant T cell clones will be assessed by a more complete analysis of the lymphokines produced after antigen-specific stimulation. These include gamma-interferon, lymphotoxin, BCGF 2 (lL 5) and further studies of lL 3 production. Helper activity will be directly assessed by determining the effects of activated tolerant T clones on antigen- specific antibody production in vitro. The cell surface phenotype of nonresponsive cells will be described, and biochemical studies will include investigations of the proteins synthesized during negative signalling and analysis of the antigen-receptor:CD3 complex. An understanding of the mechanisms involved in T cell nonresponsiveness is essential to the development of effective therapies for the treatment of autoimmune diseases, for the specific deletion of responses to allergens or to alloantigens expressed on transplanted tissues, and to avoid detrimental tolerance during immunization to tumor antigens.